1. Field of the Invention
The present invention relates to a sealing apparatus, and more particularly to a sealing apparatus having a plurality of seal lips.
2. Description of the Conventional Art
In conventional, as this kind of sealing apparatus, there has been known, for example, a sealing apparatus 52 which is used in a bearing portion 51 of a wheel suspension apparatus for a motor vehicle shown in FIG. 4. As shown enlargedly in FIG. 5, the sealing apparatus 52 is structured as follows.
First, a mounting ring 54 made of a rigid material such as a metal is provided so as to be fixedly attached to an inner periphery of an outer ring 53 in the bearing portion 51, and an elastic body 55 made of a rubber elastic material is vulcanized and bonded to the mounting ring 54. A plurality of seal lips are integrally formed in the elastic body 55. A plurality of the seal lips are constituted by an outer diameter side lip 58 which is slidably in close contact with an end surface of a flange portion 57 provided in a hub 56 corresponding to a rotation member in the bearing portion 51, an inner diameter side lip 59 which is slidably in close contact with the end surface of the flange portion 57 in an inner peripheral side thereof, and a grease lip 60 which is slidably in close contact with an outer peripheral surface of the hub 56.
In three seal lips mentioned above, the outer diameter side lip 58 and the inner diameter side lip 59 are structured such as to seal a bearing to prevent foreign materials such as muddy water, dust or the like in the outside from entering into the inside of the bearing, have an outward structure in accordance with the function thereof, and are formed such that a diameter is gradually enlarged from the base end toward the leading end. Further, the grease lip 60 is structured such as to seal the bearing to prevent a lubricating grease inside the bearing from leaking to the outside, has an inward structure in accordance with the function thereof, and is formed such that a diameter is gradually reduced from the base end toward the leading end.
The conventional sealing apparatus 52 is provided with two lips comprising the outer diameter side lip 58 and the inner diameter side lip 59 toward the outside. Accordingly, the conventional sealing apparatus 52 is structured such as to bring out an excellent muddy water resistance, however, the conventional sealing apparatus 52 has the following disadvantage.
Comparing the outer diameter side lip 58 with the inner diameter side lip 59, the former outer diameter side lip 58 is larger in its diameter, and thus an increase of rotation torque of the hub 56 is greatly affected. In spite of such the fact, a thickness t1 of the outer diameter side lip 58 is formed to be larger than a thickness t2 of the inner diameter side lip 59 (t1>t2) so as to prevent permanent deformation by fatigue of the outer diameter side lip 58 bringing out a primary sealing effect against the muddy water in the outside, in the prior art mentioned above. Therefore, as the total of two lips 58 and 59, there is a disadvantage that a sliding resistance to the rotation member such as the hub is comparatively large, whereby a torque is comparatively high.